(1) Field of the Invention
The present invention relates generally to an improved, disposable cargo container comprised of a box with extendible rotor blades that can be dropped from an aircraft to the ground, and in particular to a disposable cargo container that includes a mechanism for decelerating and orienting the container before extension of the rotor blades, thereby reducing the possibility of damage to the container.
(2) Description of the Prior Art
Numerous circumstances require the transport of various kinds of cargo to inaccessible or remote areas where ground transportation is not possible or timely. These circumstances include both military and peacetime conditions, such as providing emergency food, fuel and medical supplies to victims of natural disasters, fighting of forest fires, etc.
In many instances, the cargo can be transported to the area by helicopter, or dropped from an airplane with a parachute. However, helicopters are not always readily available, and are expensive to operate. Parachutes are also expensive, particularly when used to drop relatively small quantities of cargo, and are usually not recoverable due to the terrain and the conditions under which the cargo is dropped.
Various prior art patents since at least as early as the 1940s have proposed an alternative means involving the dropping of containers of small cargo loads from an aircraft without a parachute. Instead, the container is constructed of a disposable box with attached wings or rotor blades that extend outwardly when the box is dropped from an aircraft. The force of the air against the lower surface of these blades causes the blades to turn in the direction of their leading edges, rotating the attached box and creating lift to slow the container""s descent.
This alternative transport means, while conceptually addressing the need for inexpensive cargo delivery, has apparently found no significant application. This lack of use is believed to be attributable to two somewhat related reasons; cost effectiveness and durability.
A disposable aerial cargo container that addresses these prior art deficiencies, i.e., a container that can be manufactured at an acceptable cost while still having the required strength and durability necessary for transportation of cargo loads of up to about sixty (60) pounds or more under adverse conditions without significant damage to the cargo upon impact with the ground is described in U.S. Pat. No. 5,947,419, issued Sep. 7, 1999 to Warren et al., and incorporated herein by reference.
The Warren et al. container, like prior art containers, is comprised of a box for holding the cargo to be transported, and a plurality of wings or rotor blades having hinged roots, with the blades being deployable to a substantially horizontal attitude when the container is dropped from the aircraft. As with prior art containers, air pressure against the rotor blades causes the box to rotate and creates aerodynamic lift to slow the descent of the container. The preferred Warren et al. container includes a cargo box with a hexagonal cross-section comprised of a continuous side wall formed of six rectangular attached facets that are positioned in a hexagonal configuration, and a hexagonal end wall closing one end of the box formed by the side wall material. The open end of the container is closed with a hexagonal shaped plug type lid to enclose the cavity. Alternatively, both ends of the box can be closed and the plug placed inside the box to act as a crushable or frangible cushion of landing. The box walls, for purposes of disposability and economy, are preferably formed of corrugated paper or hardboard.
The preferred Warren et al. container includes six side panels with three or more rotor blades, one blade adjacent to every other panel depending on the number of blades used. When the container is stowed, the rotor blades are folded against the side panels and, when deployed, extend outward from the box in a substantially horizontal plane substantially perpendicular to the side panels. In order to achieve maximum lift, while still being easy to store, the blades preferably have length and width dimensions approximating the corresponding dimensions of the side panels.
While the rotor blades may be hinged at their root to one panel or side of the container box, there is a risk of separation of one or more rotors during flight, causing the container to plummet to the ground, damaging the cargo. In the Warren et al. invention, this deficiency is addressed by the use of a separate rotor blade hub positioned at the closed (upper) end of the box, with the rotor blades being hinged at their roots to the hub, instead of directly to the box. Preferably, the hub is in the shape of a metal wire or composite material frame that extends over the top and upper edges of the box. The rotor hinge points on the hub are located on the support adjacent alternating or sequential box panels, with hinge pins being used to attach the rotor blades to the hinge points of the hub. Thus, the centrifugal force exerted by the blades act upon each other through the hub and not the box. Preferably, the hub includes a common central point with connections from the central point to each of the hinge points. With this arrangement, the rotor blade""s centrifugal forces tend to act against each other to negate the stresses and loads on the box.
Upward movement of the blades during deployment and flight is limited by tethers and shock cords having their upper ends attached to the blades and their lower ends attached at the lid (lower) end of the box. The tethers may be resilient, such as a bungee cord, or a non-resilient cord of a material such as nylon. Since the tethers are also subjected to high forces, particularly during deployment, the box preferably includes a tether attachment frame that extends across the bottom wall (lid). This tether attachment frame includes attachment points to secure the lower end of each tether approximately beneath the rotor blade to which the upper end of the tether is attached. For example, the attachment frame can be in the shape of an equilateral triangle having apexes that extend beyond the periphery of the box under the alternating panel over which the panels are positioned, with one tether being attached at each apex of the triangle. Alternatively, a hub similar to the rotor hub can be placed on the bottom of the container to protect the box during handling and serve as a multiple (up to six) attach points for the tethers for all the blades.
Unlike earlier prior art rotor blades of metal or wood, the Warren et al. rotor blades are made from a planar piece of corrugated paper or polymer, either in the form of a single corrugated material sheet or a plurality of segments joined in a particular manner to provide the needed structural integrity under incurred aerodynamic and centrifugal loading, while maintaining the required economy. Each rotor blade is comprised of a lower facet, and a multi-facet upper panel with a multi-faceted forward section, a rotor spar of wood or other material, and a generally planar rear section secured to the lower panel to form an integral aerodynamically-shaped blade.
When loaded, the rotor blades are held against their respective box facets by a blade restraining strap. At the drop zone, the box is pushed from the aircraft with a static line or other means removing the blade-restraining strap. The relative wind around the box causes a lifting force to deploy the rotor blades which rotate about their hinge attach points and are snubbed by the tethers and the shock cords. The blades will be limited to a substantially horizontal orientation, i.e. plus or minus ten (10) degrees of horizontal by the tethers. In turn, the tether attach frame absorbs the tension in the tethers instead of the box. The force of the air against the lower facet of the blades, with the leading edges of the blades being lower than their trailing edges, causes the container to rotate in the direction of the leading edges, and accelerate rotationally until it achieves rotational terminal velocity, generating maximum aerodynamic lift, thereby slowing the box to its terminal vertical velocity.
While the Warren et al. cargo container is a significant improvement over prior art containers, there is still a risk of damage to the container and its contents when the container is released from the aircraft, particularly with heavy and asymmetrical loads or when the container is being deployed in high relative winds (airspeeds). As noted above, the rotor blades in the Warren et al. container are released for movement to their deployed or extended position from their stowed position as the container is released from the aircraft. As a result, the blades extend while the container is dropping rapidly, exerting considerable force on the blades and the hinged attach points. After the blades are fully extended and the container is rotating, the container will orient so that an equal force is exerted on all blades. However, when the container is dropped from a moving aircraft, the orientation of the container may be such that unequal blade forces are exerted. These unequal forces, particularly if the container is moving at a high rate of speed, may cause damage to one or more rotor blades, or prohibit their deployment.
Thus, the utility of containers constructed similar to the Warren et al. container, would be considerably enhanced, and the risk of damage decreased, if the container could be oriented and its descent slowed prior to deployment of the rotor blades. By slowing the container prior to blade deployment, the container will be farther away from the drop aircraft, insuring that the container is not struck by the aircraft.
In general, the desired results of the present invention are achieved by adding a deceleration and orientation assembly, also referred to herein as a delay assembly for brevity, as described herein in detail, to cargo containers of the type that include a cargo box with hinged blades having a stowed position against the box and a deployed position extending outwardly from the box.
The delay assembly of the present invention is generally comprised of an air resistance device, such as a drogue chute; a blade retainer adapted to secure the rotor blades in their stowed position; and a folded metering cord that has one end attached to the resistance device, an opposed end attached to the top of the container, and a segment attached to the blade retainer. Preferably, the metering cord includes a plurality of folds that are adapted to unfold in sequence.
When loading the container, the bottom cage or hub with the respective blade tethers and rotor blades attached is placed on the floor. The box is inserted into the bottom cage in its hexagonal shape and the frangible plug is inserted into the box. The payload is placed in the box on top of the plug and secured in the center of the box with packing and dunnage. The top wall of the box is closed and the rotor hub cage is placed over the top of the box. The top and bottom hubs are strapped together to maintain their relative position with each other with the box in between them. The rotor blades are then pinned in place to the rotor hinge clips on the upper hub and secured. The delay assembly and blade retaining strap is then attached and secured for transport to the aircraft for launch.
When the cargo container is discharged from the aircraft, the drogue chute or other drag device, e.g., a streamer, exerts a drag due to wind resistance, creating tension on the metering cord, sequentially opening folds of the cord, thereby slowing the descent of the container. At the same time the cord tension orients the container so that its axis is aligned with the wind direction. Following deceleration and orientation, the blade retainer is released permitting the rotor blades to open to their extended position. Since the container is moving at a slower speed, and since the force of the air is approximately equal against all of the blades, all rotor blades will deploy. Thus, the risk of damage is substantially reduced.
In a preferred embodiment, the metering cord is folded into an a plurality if S-type folds, with the folds being secured by thread that has a breaking strength below the force exerted on the metering cord during deceleration, e.g., about 15 pounds force to about 30 pounds force. The number of thread loops securing the folds is equal to twice the number of folds, with the upper or outer fold being engaged by one thread loop and each half sequential fold being engaged by a one additional thread loop. The lower fold, used to secure the blade retainer is sewn with all thread loops and therefore the last to break.
When a force exceeding the breaking strength of the thread is exerted on the cord, the single loop holding the outer fold is broken, allowing the outer fold to open. As a result, a brief drop in restraining force against the container is followed by an increased force, or tug, acting to decelerate and orient the container. The continuing force on the cord then causes the second loop to break, allowing the next fold to open with a similar effect. This sequence continues until the final thread holding the lower elongated fold is broken, resulting in pulling of the elongated fold from the blade retainer, and permitting the blades to open.